store.find() with relationship-object as parameter?

I've got two models Post.js and Category.js

Post.js

import DS from 'ember-data';

var Post = DS.Model.extend({
  title: DS.attr('string'),
  permalink: DS.attr('string'),
  body: DS.attr('string'),
  category: DS.belongsTo('category')
});

export default Post;

Category.js

import DS from 'ember-data';

export default DS.Model.extend({
  name: DS.attr('string'),
  permalink: DS.attr('string'),
  posts: DS.hasMany('post',{async:true})
});

I'd like to retrieve all posts belonging to a category via http://localhost:4200/<category_permalink>.

I have trouble to retrieve the data in the route since this doesn't work because of the category.permalink.

Route

import Ember from 'ember';

export default Ember.Route.extend({
  model: function(params) {
    return this.store.find('post', { category.permalink: params.category });
  }
});